As the advance of technology, portable electronic devices (e.g. mobile phones, tablet computers and notebook computers, etc.) and wireless transmission devices (e.g. USB connection devices, wireless network cards and access points) are becoming more and more powerful, so these devices' requirements for antennas are also becoming stricter.
Currently, planar inverse-F antennas (PIFA) of compact size and with great transmission performance have been comprehensively applied to portable electronic devices and wireless transmission devices. Antennas may need several operating frequency bands in order to satisfy the requirements of different frequency bands. However, the antenna characteristics of the currently available dual-band antennas cannot be easily adjusted because of the limitations in their structure designs; for the reason, antenna designers always need to spend a lot of time on adjusting the structures of these antennas in order to realize desired antenna characteristics.
In addition, the isolation is another important factor capable of influencing the performance of antennas. However, the isolations of the currently available dual-band antennas usually cannot meet the requirements because of the limitations in their structure designs, so the performances of these antennas are influenced accordingly.
Therefore, it has become an important issue to provide a dual-band antenna capable of improving the limitations of the currently available antennas.